The present invention relates to a broadcasting receiver and, more particularly, to a broadcasting receiver having a power-saving (sleep) mode for reducing power consumption on standby, where precision of an internal timer is improved.
In recent years, plural broadcasting satellites have been launched, and thereby digital broadcastings using the satellite waves have been started by plural broadcast distributors. In order to receive services of the broadcastings, a set top box (hereinafter, also referred to as STB) should be installed as a receiver, which is to be a decoder for decoding compressed signals of the received broadcasting and converting the same into signals which can be displayed on a display unit such as a CRT.
FIG. 5 is a block diagram mainly illustrating a clock generation unit in a STB as the above-described receiver, which is shown in the standards of MPEG, SO/IEC 13818-1 generic coding of moving pictures and associated audio: systems, Annex D.0.3 System Time Clock recovery in the. decoder. In the figure, reference numeral 10 denotes a capture PCR for capturing a PCR (Program Clock Reference) indicating a broadcasting time for each program, which is included in a transport stream. Numeral 11 denotes a subtracter for generating a difference between an output of an STC counter, which will be described later, and an output of the capture PCR 10. Numeral 13 denotes a low-pass filter for cutting high frequency components that are above a predetermined value so as to prevent an oscillation circuit 15, which will be described later, from significantly fluctuating (diverging) when the difference is abruptly changed. Numeral 14 denotes a D/A converter for converting a signal which passed through the filter 13 into an analog signal. Numeral 15 denotes an oscillation circuit, such as a voltage controlled oscillator (VCO), oscillation frequencies of which are controlled by an analog signal (voltage). Numeral 16 denotes an STC (System Time Clock) counter operating with a frequency signal (clock) output from the oscillation circuit 15 and functioning as an internal timer in the system. In addition, around this clock generation unit, circuits such as a tuner for selecting a channel or a decoder for decoding data are placed.
Using the above-described structure, a predetermined frequency signal is generated on the basis of a PCR indicating a broadcasting time for each program, which is included in the transport stream, and the internal timer in the system is operated. That is, the PCR detected by the capture PCR 10 is converted into an analog signal by the D/A converter 14, after its high frequency components above the predetermined value are cut off by the filter 13. Then, the oscillation circuit 15 receives the converted analog signal (voltage) as an input and outputs a frequency signal, and the STC counter 16 in the latter stage operates with the frequency signal. Then, a difference between the output of the STC counter 16 and the output of the capture PCR 10 is generated by the subtracter 11. By adjusting a loop from the subtracter 11 to the STC counter 16 so as to have the difference of xe2x80x9c0xe2x80x9d, a clock in synchronization with an input signal can be reproduced.
Anyhow, in recent years, there are some household electrical appliances in which the power consumption during standby when they are not used is not much smaller than that during operation.
Also in the STB, as in a television apparatus, it is considered to be preferable that unnecessary elements, such as a tuner or a decoder, should be powered off when they are not used, i.e., they are not in operation. Therefore, some STBs are constructed so as to be in the sleep mode (referred to also as an operation standby state) till a reserved processing start time. However, since reservation processings are performed with respect to playback/recording or the like in the STB, when the power is turned off for a long time, an error occurs in the internal timer and the reserved processing cannot be executed at a correct time.
The conventional broadcasting receiver is constructed as described above, and it does not have a structure for realizing lower power consumption on standby or, even when it has a structure which can put the STB into the sleep mode for the lower power consumption, it cannot perform the reserved processing at a correct time due to the error in the internal timer.
The present invention is made to solve the above-described problems and it is an object of the present invention to provide a broadcasting receiver which can perform the reserved processing at a correct time even when the STB is put into the sleep mode.
A broadcasting receiver according to an embodiment of the present invention, which generates a clock of a predetermined frequency on the basis of a reference signal included in digital data including time-axis information and has an internal timer operating with the clock, comprises: reference signal detection means for detecting the reference signal; clock generation means for generating a clock of a frequency on the basis of the reference signal; counter means for counting the clock; difference generation means for calculating a time difference between output of the counter means and the reference signal; and control means for holding the output of the clock generation means when the receiver is changed to an operation standby state.
According to the present invention, when the receiver is in the operation standby state, the reference signal detection means detects the reference signal, the holding operation of the control means is released, and the receiver is put into an operation state for a prescribed time.
According to the present invention, a transport stream is utilized as the digital data including the time-axis information and a PCR (Program Clock Reference) indicating a broadcasting time for each program is utilized as the reference signal.
According to the present invention, a transport stream is utilized as the digital data including the time-axis information and a TDT (Time and Data Table) indicating a broadcasting time for each program is utilized as the reference signal.
As described above, according to the broadcasting receiver of the present invention, when the STB is changed into the sleep mode, a difference is immediately held by the control circuit and the oscillation circuit is controlled on the basis of the difference. Therefore, even in the sleep mode when the PCR cannot be detected, the great divergence of the oscillation frequencies can be avoided, whereby processings such as reserved processings can be performed on time.
In addition, the receiver is started at a uniform time interval during the sleep mode, receives the transport stream to detect the reference signal, and thereby occasionally corrects the time. Therefore, the precision of the internal timer can be further improved.